The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Scanned images can be smoothed or sharpened using an image filter in order to improve image quality. Scanned half-tone images—images that simulate continuous tone imagery by using dots of varying size, tone, shape, and spacing—are improved by smoothing. But scanned text documents and continuous tone (contone) images—images with contiguous dots that cause the appearance of a continuous tone—can be improved by sharpening. Image smoothing reduces differences between adjacent dots, essentially filtering out high frequency components in the image, in order to generate a smoother image. Image sharpening amplifies high-frequency components in the image in order to increase the detail of the image. A conventional scanner application allows the user to control image processing settings—sharpening or smoothing—based on the type of image being scanned.
But some images have multiple region types, such as regions that are half-tone, regions that are contone, and regions that are text. And using a single filter setting on such documents results in filter mismatch on some regions, a loss of data, and reduced image quality. This is especially true of images that are scanned, printed, and then scanned again.